High quality factor, integrated inductor and production method thereof

ABSTRACT

The integrated inductor comprises a coil of metal which is formed in the second metal level. The coil is supported by a bracket extending above spaced from a semiconductor material body by an air gap obtained by removing a sacrificial region formed in the first metal level. The bracket is carried by the semiconductor material body through support regions which are arranged peripherally on the bracket and are separated from one another by through apertures which are connected to the air gap. A thick oxide region extends above the semiconductor material body, below the air gap, to reduce the capacitive coupling between the inductor and the semiconductor material body. The inductor thus has a high quality factor, and is produced by a process compatible with present microelectronics processes.

TECHNICAL FIELD

[0001] The present invention relates to a high quality factor, integrated inductor and a production method thereof.

BACKGROUND OF THE INVENTION

[0002] As is known, inductors are key components of the operating blocks of a radio-frequency circuit. Their critical parameters comprise the inductance value L, the quality factor Q, and the resonance frequency f. Many applications, such as GSM cellular communications systems, require inductors which have inductance L of 1-10 nH, a quality factor Q of at least 10, and a resonance frequency which is far greater than 1 GHz.

[0003] Integrated inductors made of aluminum, which have a quality factor Q of 3, can easily be produced by means of standard microelectronics processes. The quality factor Q is however limited by the parasitic capacitance towards the substrate, and by the resistance of the inductor itself. Consequently, it is not possible at present to produce integrated inductors of semiconductor material which have a high quality factor. For applications which have high requirements, discrete inductors external to the integrated silicon device are used.

SUMMARY OF THE INVENTION

[0004] An object of the invention is thus to provide an inductor which has a high quality factor.

[0005] The present invention provides a high quality factor integrated inductor and production method thereof. In one embodiment of the present invention, the integrated inductor comprises a coil of conductive material wherein said coil is supported by a bracket extending above and spaced from a semiconductor material body by an air gap. The bracket is carried by the semiconductor material body through support regions.

[0006] To enable the present invention to be understood, a preferred embodiment is now described, purely by way of non-limiting example, with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 is a transverse cross-section through a wafer of semiconductor material, in a first production step of the present inductor.

[0008]FIG. 2 is a view from above of part of the wafer in FIG. 1.

[0009]FIG. 3 is a transverse cross-section of the wafer in FIG. 1 in the inductor area and on an enlarged scale, in a subsequent production step.

[0010]FIG. 4 is a see-through view from above of the wafer in FIG. 3.

[0011]FIG. 5 is a cross-section similar to FIG. 3, in a subsequent step.

[0012]FIG. 6 is a see-through view from above of the wafer in FIG. 5.

[0013]FIG. 7 is a cross-section similar to that in FIGS. 3 and 5, in a subsequent step.

[0014]FIG. 8 is a transverse cross-section of the device at the end of production, seen along the cross-sectional plane VIII-VIII in FIG. 7.

[0015]FIG. 9 is a view from above of the device in FIG. 8, with layers removed.

DETAILED DESCRIPTION OF THE INVENTION

[0016] The present production method allows integration of an inductor to form an integrated electronic device of semiconductor material (e.g., silicon) which has electronic components of the MOS or bipolar type. The method begins with production steps known for forming electronic components. Referring to FIG. 1, on a substrate 1 of P-type, an epitaxial layer 2 of N-type is grown, obtaining a semiconductor material wafer 3; across a surface 7 of the epitaxial layer, thick field oxide regions are formed in order to delimit the active areas; in particular, a thick oxide region 4 extends in the area on which the inductor will be formed (inductor area 6). Then, in the epitaxial layer 2, junction isolation regions 5 of P-type are formed, extending from the surface 7 of the epitaxial layer 2 to the substrate 1, and in the epitaxial layer 2, conductive regions necessary for forming electronic components are formed. In particular, FIG. 1 shows an NPN transistor 8, having a collector contact region 9 of N⁺-type, a base region 10 of P-type, and an emitter region 11 of N⁺-type.

[0017] Subsequently, on the surface 7 of the epitaxial layer, a surface dielectric layer 14 (for example BPSG, Boron Phosphorous Silicon Glass) is deposited, and contacts are opened by means of a masking and selective removing step. Then, a first metal layer is deposited and defined, comprising for example aluminum-silicon, or aluminum-silicon-copper; thereby contact electrodes 15 for the components, and, in the inductor area 6, a sacrificial region 16 a and a first connection line 16 b are formed, region 16 a and line 16 b extending above the thick oxide region 4. Thus, the intermediate structure of FIG. 1 is obtained, wherein the sacrificial region 16 a has an approximately polygonal shape with a plurality of peripheral extensions 17, providing the sacrificial region 16 a with the shape of a “toothed wheel”, as can be seen in the view from above in FIG. 2, relative to the inductor area 6 alone. As can be seen in FIG. 2, the sacrificial region 16 a has a slot 18 which extends radially, and inside which there extends part of the first connection line 16 b, which is spaced from the sacrificial region 16 a.

[0018] Then an intermediate dielectric layer 20 (FIG. 3) is deposited and removed from the areas of the peripheral extensions 17, from the end of the first connection line 16 b which is in the center of the sacrificial region 16 a, and from the connection vias for the electrical components (not shown). In particular, at the end of the first connection line 16 b, the intermediate dielectric layer 20 forms an aperture 35, and at the peripheral extensions 17 it forms apertures 36.

[0019] A second metal layer 21 of Al—Si or Al—Si—Cu or Cu is then deposited. In particular for Al—Si or Al—Si—Cu, this second metal layer 21 is deposited by sputtering, whereas for copper, it is grown electrolytically. The second metal layer 21 is in direct contact with the first metal layer 16, in the areas in which the intermediate dielectric layer 20 has been removed, in particular at the apertures 36, the aperture 35, and where the vias (not shown) have been formed. Subsequently, the second metal layer 21 is shaped, and forms a contact region 21 a extending inside the aperture 35; a coil 21 b of the inductor extending, spiral-shaped, above the intermediate dielectric layer 20, from the contact region 21 a towards the exterior; and a second connection line 21 c extending without interruption from the coil 21 b, as shown in FIG. 4, in which broken lines also represent the sacrificial region 16 a and the first connection line 16 b. In this step, in the apertures 36, etch regions 21 d are formed, which are approximately in the shape of “plugs”, providing the structure in FIG. 3; in addition (in a known and therefore not shown manner), a second electrical connection level of the circuit is formed.

[0020] Subsequently a passivation layer 25 of dielectric material is deposited and removed selectively at contact pads (not shown) of the circuit and at the etch regions 21 d, which remain uncovered, as shown in FIG. 5. Then a protective layer 26, for example TEOS (tetraethylorthosilicate), with a thickness of 2000 A is deposited and removed at the etch regions 21 d, forming apertures 33 which extend through the protective layer 26 and the passivation layer 25, as shown in FIG. 6, in which the sacrificial region 16 a and the first connection line 16 b are again represented by a broken line. The metal regions are then wet etched through the apertures 33; thus removing all the etch regions 21 d and the sacrificial region 16 a below the intermediate dielectric layer 20. Then the structure of FIG. 7 is obtained, the Figure showing an air gap 28, the shape of which corresponds exactly to the above-described sacrificial region 16 a which is shown in FIG. 2. At this stage, the protective layer 26 protects the passivation layer 25 against etching.

[0021] Finally, the protective layer 26 is removed from the entire surface (blanket removal). Then the final structure of FIG. 8 is obtained, wherein the coil (indicated at 40) of the inductor is carried by a bracket 20 a formed from the intermediate dielectric layer 20, and is supported at the areas 20 b which are delimited laterally by the apertures 36, as can be seen in FIG. 9, which shows a schematic view from above and on a reduced scale of the finished device, wherein the passivation layer 25 has been omitted and the periphery of the air gap 28 and the first connection line 16 b are indicated by a broken line. As can be seen, the bracket 20 a is also in contact with the wafer 3 at the narrow strip which surrounds the first connection line 16 b (above the slot 18, and indicated as a portion of electrical isolation 20 c).

[0022] This provides an integrated device 39, which comprises an integrated inductor 40, in addition to integrated electronic components such as the transistor 8. The integrated inductor 40 has a high quality factor, owing to the presence of an air gap, indicated at 28 in FIGS. 7 and 8, between the bracket 20 a and the surface dielectric layer 14, and to the presence of a thick field oxide layer 4, which further reduces the coupling of the inductor and the substrate.

[0023] The production method described is compatible with the usual production processes used in the microelectronics industry, and thus has the advantages of reliability, controllability and repeatability which are typical of these processes. It requires only an additional mask for shaping the protective layer 26, compared with the standard processes with two metal levels, since the first metal level is also used to form the sacrificial region, and the second metal level is used to form the inductor; it therefore has costs which are comparable with, or only slightly higher than those of the standard processes.

[0024] Finally, it will be appreciated that many modifications and variants can be made to the inductor and the production process described and illustrated here, all of which come within the scope of the inventive context as defined in the attached claims. 

1. An integrated inductor, comprising a coil of conductive material wherein said coil is supported by a bracket extending above, and spaced from a semiconductor material body by an air gap, said bracket being carried by said semiconductor material body through support regions.
 2. The inductor according to claim 1 wherein said bracket is made of dielectric material.
 3. The inductor according to claim 1 wherein said support regions comprise connection portions disposed peripherally on said bracket, and separated from one another by through apertures connected to said air gap.
 4. The inductor according to claim 1 wherein said inductor comprises an electrical isolation portion extending between said bracket and said semiconductor material body, from a central area towards a peripheral area of said bracket.
 5. The inductor according to claim 4 wherein said electrical isolation portion is made of dielectric material, and surrounds above and laterally an electrical connection line extending on said semiconductor material body, said connection line being connected to said coil through a contact region extending through an aperture of said bracket.
 6. The inductor according to claim 1 wherein said inductor comprises a field oxide region extending above said semiconductor material body and below said air gap.
 7. A method for production of an integrated inductor, comprising: forming a sacrificial region on a semiconductor material body; forming a support region on said sacrificial region; forming an inductor component on said support region; forming, laterally to said inductor component, apertures (33, 36) extending as far as said sacrificial region; and removing said sacrificial region through said apertures.
 8. The method according to claim 7 wherein the step of forming a sacrificial region comprises the steps of depositing a first metal layer on said semiconductor material body and shaping said first metal layer.
 9. The method according to claim 7 wherein the step of forming a support region comprises the steps of depositing an intermediate dielectric layer and removing selective portions of said intermediate dielectric layer.
 10. The method according to claim 7 wherein the step of forming an inductor component comprises the steps of depositing a second metal layer and shaping said second metal layer, thereby forming a spiral structure.
 11. The method according to claim 10 wherein before forming the inductor component, the step is carried out of forming first apertures laterally to said support region, and in that the step of forming apertures comprises the steps of: depositing a protective layer (25, 26) on said inductor component; selectively removing portions of said protective layer (25, 26) laterally to said inductor component, to form second apertures; selectively removing portions of said second metal layer from said first apertures, said first and second apertures (33, 36) forming said apertures.
 12. The method according to claim 7 wherein simultaneously with the step of forming said inductor component, the step is carried out of forming etch regions of metal, in a peripheral area of said support region and in direct contact with said sacrificial region, and in that the step of forming apertures (33, 36) comprises the step of removing said etch regions.
 13. The method according to claim 12 wherein the steps of removing the etch regions and removing the sacrificial region are carried out in a single wet etching step.
 14. The method according to any claim 7 wherein before the step of forming a sacrificial region, the step is carried out of forming a field oxide region on said semiconductor material body.
 15. The method according to claim 7 wherein before the step of forming a sacrificial region, the step is carried out of integrating electric components in said semiconductor material body.
 16. A semiconductor device having an inductor integrated on a semiconductor material body, said device comprising: a bracket extending above, and spaced apart from, the semiconductor material body by an air gap, said bracket being made of dielectric material and being supported by the semiconductor material body through support regions; and a conductive coil placed over and supported by said bracket.
 17. The device of claim 16 wherein the support regions comprise connection portions disposed peripherally on said bracket and separated from one another by gap apertures in communication with said air gap.
 18. The device of claim 16, further comprising an electrical isolation portion extending between said bracket and said semiconductor material body and from a central area towards a peripheral area of said bracket, said electrical isolation portion being made of dielectric material.
 19. The device of claim 18 wherein said electrical isolation portion surrounds above and laterally an electrical connection line extending on said semiconductor material body, said connection line being connected to said coil by a contact region extending through a contact aperture of said bracket.
 20. The device of claim 16, further comprising a dielectric region extending above said semiconductor material body and below said air gap.
 21. The device of claim 20 wherein said dielectric region comprises: a field oxide region deposited over the semiconductor material body; and a dielectric layer deposited over said field oxide region.
 22. The device of claim 21 wherein said dielectric layer is a BPSG layer.
 23. A method for manufacturing a semiconductor device having an integrated inductor, the method comprising: forming a dielectric layer on a semiconductor material body; forming a sacrificial region and an electrical connection line on the dielectric layer; forming a support region of dielectric material on said sacrificial region; forming an electrically conductive coil on said support region; forming apertures peripherally and separated from each other on said support region and extending as far as said sacrificial region; and removing said sacrificial region through said apertures to form an air gap under the support region.
 24. The method of claim 23 wherein the step of forming a dielectric layer comprises: forming a field oxide layer over the semiconductor material body; and forming a silicate glass layer over the field oxide layer.
 25. The method of claim 23 wherein the step of forming the sacrificial region and the connection line comprises depositing a first metal layer, and the step of forming the coil comprises depositing a second metal layer. 